Cambridge Dictionaries online Cambridge Dictionaries online

The most popular online dictionary and thesaurus for learners of English

English definition of “lunacy”

lunacy

noun [U]     /ˈluː.nə.sɪ/
stupid behaviour that will have bad results: It would be lunacy to try to climb the mountain in this weather. It was sheer lunacy spending all that money.Of unsound mindStupid and silly old-fashioned mental illnessOf unsound mindStupid and silly
(Definition of lunacy noun from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
Focus on the pronunciation of lunacy

Browse related topics

You are looking at an entry to do with Of unsound mind, but you might be interested in these topics from the Psychology, psychiatry, & psychoanalysis topic area:

Definitions of “lunacy” in other dictionaries

Word of the Day

closeness

the quality of knowing someone very well, liking them a lot, and wanting to spend a lot of time together

Word of the Day

Blog

Read our blog about how the English language behaves.

Learn More

New Words

Find words and meanings that have just started to be used in English, and let us know what you think of them.

Learn More